Each individual user who wants access to the files on the USATLAS and CERN grids must gain permission to do so. There's no Nevis-wide approval or script -- you must do it on your own.

The procedure to access files on the Grid breaks down into two phases: a lengthy one-time set-up procedure, and the commands you must issue every time you wish to access the Grid.

1. Setting up Grid access

   Warning: the initial set-up takes time. You should allow 2-3 days to make your way through the bureaucracy of approvals. If you're consulting this page because you need to access files right away, the best advice I can give you is to ask someone who already has Grid access to get the file for you.

   The steps to set up Grid access are:

   • Request a certificate from the DOEGrids Certificate Authority.

     You must do this from a web browser that can handle certificates. Most modern web browsers can do so; if you use a text-based browser or you're still using Mosaic you'll have a problem.

   • The directions in the previous step will take you to the DOEGrids Certificate Manager.
     • Under "Affliation", select "PPDG".

     • For the "Name of Sponsor", put "John Parsons". You can get John's e-mail address and phone number from the Nevis phone list.

     • Under "Additional comments", I put "Needed to enable access to ATLAS Grid files at Nevis Laboratories, Columbia University." Hopefully that will work for you as well. Do not leave this field blank; otherwise you'll just a message back saying that your request was denied.

   • Go back to the DOEGrids Certificate Authority page after you receive the e-mail approving your certificate.

     By following the directions on that page, you'll import your certificate into your web browser, then export it and convert for use by Globus.

     Be careful when you assign the passwords for your certificate. For example, you'll need the "export password" every time you type the globus-proxy-init command as described below. If you forget your passwords, there's nothing anyone can do; you may have to re-export or re-request a certificate (depending on which password you forget). I advise you to use the same password as your login.

     Of course, if you're strict about security, you should use different passwords -- but don't say you weren't warned!

   • Next, you'll need to join the ATLAS Virtual Organization (VO). In fact, you'll probably want to join two: USATLAS (the grid3/OSG virtual organziation), and CERN ATLAS (the LCG virtual organization).

     Start with the Brookhaven USATLAS VO web page. This will send you to LCG User Registration.

     After reading the information referenced on these pages, you'll finally be asked to fill out a registration form.

     • Your "Institute" is, of course, "Nevis Labs, Columbia University".

     • From the "VO" list, select "Atlas LCG2 and OSG".

   • After submitting the VO registration, you're likely to get back an e-mail asking for more information. I suggest you forward the message to usatlas-vo@bnl.gov, with a CC to the originator of the message, and to John Parsons (the last because you may get a request for a digitally-signed message from your supervisor). In the message, state that you need Grid access to the ATLAS files to do your analysis at Nevis.

   • Hopefully, after you've gone through all the previous steps, you'll receive e-mails informing you that your membership to the two VOs has been approved.

2. How to fetch files from the Grid.

   We have not installed Globus at Nevis. Instead, we use the installation at BNL. This means that you need to use a machine with AFS to issue the following commands:

   # csh-style setenv GLOBUS_LOCATION /afs/usatlas.bnl.gov/Grid/vdt/current/globus source $GLOBUS_LOCATION/etc/globus-user-env.csh # sh-style export GLOBUS_LOCATION=/afs/usatlas.bnl.gov/Grid/vdt/current/globus source $GLOBUS_LOCATION/etc/globus-user-env.sh # You'll be prompted for your certificate "export password" with this command: grid-proxy-init # The above commands set up Grid access, and must be entered once per # login session. Here's an example of how to fetch a file: globus-url-copy -p 3 -vb \ gsiftp://aftpexp.bnl.gov/usatlas/workarea/wdeng/data/Y01345.9.al \ file:///tmp/testcopy

   The last command above will copy the Grid file Y01345.9.al to /tmp/testcopy on your local machine.

   Here's more documentation on the globus-url-copy command. The complete Globus documentation may also be useful.

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